In a heavy ion or proton nucleus collision the total transverse energy, , is a measure of the energy liberated by the deceleration, or “stopping power" of the colliding nucleons while \(/y\)  measures the
total energy carried by the system of particles or medium, produced in the collision, which is moving with longitudinal rapidity \(y\)  [1]}.
In heavy ion collisions the energy density, \(\epsilon _\text{BJ}\) , of this medium at proper time
\(\tau _0\) 
shortly after the impact of the two nuclei
can be estimated using the Bjorken formula
\(\epsilon _\text{BJ}=\frac{}{y}\frac{1}{\tau _0 A_\perp },\) 
